I understand how difficult it is to keep your kid's teeth clean and cavity free. My 4 year old daughter has a very prominent streak of independence and she always insist she does the brushing. We have a deal... she brushes then I brush. I recommend this to all parents until the children are old enough to use the brush effectively typically around age 6. Teaching kids the right way to brush is just as important how often they do. Rule of thumb is morning and evening and no snacks or drinks other than water afterwards.
Brushing needs to begin even before the teeth erupt. Infants can still collect bacteria and even fungus on the gums, palate, and tongue. Small fingertip appliances that swab the tissues gently work the best. As the teeth erupt, get in the habit of lightly brushing them at least once per day. When the child begins solid food regimens, traditional brushing of the teeth becomes even more important. Although cute at times, it is advisable to avoid refined carbohydrates (sugar) and soda's as this creates habits that can readily cause an uptick in the rate of cavities. Baby bottle decay is a severe form of early childhood cavities caused by the nighttime use of bottles in children who have erupted teeth. As the child sleeps, the bottle stays in and if milk or juice products are present, cavities form very readily. Unfortunately, most of these cases require teeth to be prematurely extracted placing the child at risk for major orthodontic and functional concerns in the future.
As the child approaches their 2nd birthday, the last of the primary molars erupt and the contacts between the teeth begin to close. Flossing becomes more important as the teeth start to touch. Also, it is advisable to begin taking X-rays of the teeth on a routine basis. This establishes great habits that can carry through their lifetime. Kids that visit the dentist regularly tend to be more attentive to their home care and have fewer restorative needs.
So keep them squeaky clean. And don't forget that your teeth are important too :)